We actually used it more less to warm the battries on the truck up. As it had decided to stop right across a road junction it was desperation measures. I've actually just finished playing with the thing. I'm still trying all angles to get an old 6 volt battery up. So I put it in series with a 12 volt and wound the old Chore Horse up. I will point out it was outside to allow for any hydrogen to gas. The output measured at full blast across the sytem was 20.26 volt starting at 1 amp then going up to 20 as the system heated up. Unlaode voltage measuered at 30. Unfortunatley though two cells of the 6 volt started to gas one didn't , so it has breathed it's last. The manual says that you can use 250 feet of cable from the set to battries, so it is a powerful little beast.
Considering the thing has sat in the shed for about two years, was dragged out filled with fuel , given a whiff of Easy Start, and away it went, they are tough old beasts. I have tried to pul start it, took about a week for the shoulder strain to go away, with no starting! So now I put it on a charged 12 volt and use the little red button. This reverses the flow so the rotary dynamo becomes a starter motor. Once running it self sustains on the magneto. The engine is fixed on a mechanical govenor. Voltage and ampage output is variable by a conrtrol knob. Though I do keep a seperate meter across the system.
Worth having about the workshop if you can get one.